1. Field of the Invention
The present invention relates to a pulse generator having a field plate differential sensing element, and more particularly to a clock disc which consists of soft magnetic material and which has teeth arranged in asymmetrical graduation at the periphery thereof.
2. Description of the Prior Art
As the write/read heads in disc memories do not exhibit a stable flight characteristic until a specific speed of rotation is attained, and only then can be allowed to be loaded into the stack of discs, and on the undershooting of the limiting rotating speed must immediately be unloaded again, it is necessary to monitor the rotating speed of the stack of discs and the direction of rotation in disc memories. When write/read heads are loaded, an incorrect direction of rotation of the stack of discs will, because of the then negative angle of pitch of the flying body, lead to the immediate destruction of the write/read heads and of the stack of discs. The deceleration of the stack of discs on disconnection also necessitates the monitoring of the existence of a rotating movement of the stack, as it is this movement which is evaluated as a criterion for the connection of the retarding potential to the drive motor during the disc connection process. Such a monitoring signal can also be used for an optical display of the presence of a rotating movement of the stack, and for the mechanical unlocking of the device cover and sundry ancillary operations.
The problem of establishing a rotating movement, the direction of rotation and the rotating speed of a component occurs not only, however, in the case of stacks of discs in disc memories, but wherever rotating components are to be monitored in respect of rotating speed and direction of rotation.
In order to establish the rotating speed, the direction of rotation and the existence in itself of a rotating movement, it has become known in the art to utilize a disc, called a clock disc, which is connected to the rotating component and whose movement and position is sensed by a measuring sensing component and is analyzed in an analysis circuit.
It has also become known to establish the rotating speed and the direction of rotation with the use of arrangements which consists of a permanent magnet and a field plate differential sensing component. In these arrangements, magnetic control fields are not, as is usually done, supplied from the exterior of the arrangement, but a soft magnetic gear arrangement influences the inner magnetic circuit of the field plate differential sensing element in such a manner that changes in air gaps give rise to a reversal of flux and therefore give rise to changes in reluctance in the field plates, as a result of which high signal voltages per tooth are produced.
In devices which operate with field plate differential sensing components of this type, the teeth at the periphery of the clock discs are generally recesses of rectangular or trapezoidal shape which extend into the disc from the periphery. Teeth having this shape are advantageous wherever a pulse train disc must possess a plurality of teeth. If, however, as for example in the case of disc memories, it is expedient for the clock disc to have only a single tooth, or a few teeth, arranged in asymmetrical graduation, because of the resultant imbalance of the disc, it is no longer readily possible to utilize this known design of the clock disc.